The previous combined immunological studies of patients with systemic lupus erythematosus (SLE) and rheumatoid arthritis (RA) will be pursued further. The long term investigation of different immune complexes and their role in the tissue injury of these diseases will be continued. Special attention will be paid to the elucidation of additional basic immune defects especially in the SLE patients. Several potential clues to possible infectious agents that may be specifically or secondarily involved will be explored in a variety of different ways. Possible relationships to the new dominant histocompatibility patterns in these diseases will be sought with emphasis on those involving the new B cell alloantigen system.